1. Field of the Invention
The present invention relates to semiconductor wafers, semiconductor thin film devices, and a method of manufacturing semiconductor thin film devices.
2. Description of the Related Art
Nitride semiconductor devices and SiC semiconductor devices are known which are formed on an Si substrate for excellent heat dissipation and electrical characteristics. Japanese Patent Application Publication No. 2005-129876 discloses the following technology. A porous Si layer is formed on a first Si substrate (growth substrate) or, i.e., Si (100) substrate, a BP buffer layer is formed on the porous Si layer, then a GaN/AlGaN layer is formed on the BP buffer, and finally an Al/Ti layer is formed on the GaN/AlGaN layer. The structure is then bonded to a second Si substrate (support substrate) with the Al/Ti layer in direct contact with the second Si substrate. Then, the entire structure is divided at the porous Si layer from the first Si substrate. The publication also discloses a technology in which the BP layer and GaN layer are removed from the structure and then a Ti/Al/Pt electrode is formed on the uppermost layer.
After transferring the structure formed on the first Si substrate onto the second Si substrate, the first Si substrate is removed and the buffer layer is removed by lapping before forming an electrode thereon. This implies that the order in which the respective layers are formed on the second Si substrate is reversed with respect to that when the layers are formed on the first Si substrate.
However, this process presents a problem in that some components are difficult to isolate. In addition, a device formed on a growth substrate may not be transferred onto another substrate without difficulty. When components are to be formed after a semiconductor layer has been bonded to another substrate, if the component isolation process includes a high temperature heating process, an Al/Ti layer, for example, may not be reliably bonded. Highly doped nitride semiconductor and SiC are still difficult to achieve high activation by their nature, resulting in difficulty in forming low-resistance contacts between these semiconductor materials and metal electrodes.